In an aircraft gas turbine (et) engine, air is drawn into the front of the engine, compressed by a shaft-mounted compressor, and mixed with fuel. The mixture is combusted, and the resulting hot combustion gases are passed through a turbine mounted on the same shaft. The flow of gas turns the turbine by contacting an airfoil portion of the turbine blade, which turns the shaft and provides power to the compressor. The hot exhaust gases flow from the back of the engine, driving it and the aircraft forward. There may additionally be a bypass fan that forces air around the center core of the engine, driven by a shaft extending from the turbine section.
The compressor, the turbine, and the bypass fan have a similar construction. They each have a rotor assembly including a rotor disk and a set of blades extending radially outwardly from the rotor disk. The compressor, the turbine, and the bypass fan share this basic configuration. However, the materials of construction of the rotor disks and the blades, as well as the shapes and sizes of the rotor disks and the blades, vary in these different sections of the gas turbine engine. The blades may be integral with and metallurgically bonded to the disk, forming a BLISK (“bladed disk”, also sometimes known as an “integrally bladed rotor” or IBR), or they may be mechanically attached to the disk.
During manufacture or service, one (or more) of the blades of the BLISK may be damaged, as for example by the impact of particles entrained in the gas flow that impinges on the blade. If the damage is sufficiently severe so that the location on the blade is below its minimum specified thickness, the blade must be repaired. In the repair, the damaged area is built up with a metallic deposit. The BLISK is then heat treated to relieve residual stresses. The repair process heats the BLISK and causes the formation of an oxygen-enriched, reduced-ductility alpha case in titanium-alloy BLISKs. The alpha case must be removed, typically by etching. If the blades of the BLISK are repaired multiple times, the disk may be etched so many times that other portions of the BLISK are reduced below their minimum dimensions. Repeated repairs are therefore not possible.
There is therefore a need for an approach that permits BLISKs to be repaired multiple times, without significant degradation in properties and without a reduction in dimensions to below the minimum specified values. The present invention fulfills this need, and further provides related advantages.